Drying Of Raw Materials: Complete Technical Guide

Drying of raw materials (module 04 of the cement training series, 33 pages) is the training module of the moisture: the water that rides in the limestone and the clay, the energy it costs, and the machines and the systems that remove it before the mill: the module teaches the drying in the process chain: why the moisture matters, how the drying is measured, the types of the dryers (the rotary dryers, the flash dryers and the drying inside the raw mill with the kiln gases), and the control of the dried product: it is the module of the wet season, of the sticky clay and of the heat the plant recovers from its own kiln.

The Complete Cement Technical Package (931 files: books, courses, Excel tools and presentations, $249.99 one-time, instant download via the PayPal payment) delivers this module with its series: after the crushing and before the raw grinding: the drying is the hinge of the raw department: this guide presents the content of the module: the moisture, the dryers, the circuits and the energy of the drying stage.

1. Why the Drying Is a Chapter of Its Own

The raw materials of the plant are never dry: the limestone of the quarry carries its free water (1–6%), the clay and the marl of the humid regions arrive with 10–25% of the moisture, and the rainy season changes the numbers weekly: the raw mill and the raw meal of the plant cannot work with the arbitrary water: the mill feed has its moisture window (the drying capacity of the mill system, typically 8–14% for the air-swept systems and much less for the others), and the kiln feed must be consistent: the drying chapter exists because the water is the enemy of the chemistry control and of the heat balance: the module explains: every kilogram of the water that enters the system must be evaporated, and the evaporation costs about 2,600 kJ per kilogram: the drying is an energy department of the plant, not a footnote.

In the formation series the module sits in its natural place: after the raw materials and the crushing (the wet rocks arrive) and before the raw mill and the kiln (the dry meal leaves): the trainee of the raw department reads the module at the same time as the moisture of his own plant: the module gives the numbers, the machines and the discipline.

2. The Moisture and the Measurement

The module begins where the plant begins: with the water content of the materials:

• The free water and the bound water: the module distinguishes: the surface and the capillary water (the free, removable by the drying) and the combined water of the minerals (the clay structure, the carbonates: removed only in the kiln): the drying of the module concerns the free water: the bound water is the territory of the kiln course.
• The measurement: the classic oven-dry method (the sample, the 105–110°C, the percentage of the loss) and the rapid methods of the field (the moisture balances and the probes): the module: the moisture of the day: the frequency: the quarry and the mill samples: the module’s sampling plan.
• The moisture of the components: the limestone 1–6%, the clay 8–25%, the sand, the correctives, the fly ash: the module’s table of the typical values: the wet seasons of the plants: the module: the moisture is a moving input and the plant plans it like the chemistry.
• The consequences of the excess: the sticky screens and the clogged chutes, the mill overloads and the coating, the loss of the mill capacity, the kiln heat losses and the unstable feed: the module: the moisture pays in the equipment before the energy bill: the complete accounting of the water.

The moisture chapter fixes the language: the free and the bound, the percent of the day, the costs: the trainee leaves the first pages with the reflex of reading the moisture of every material that enters the department: the same reflex the operators keep all their careers.

2. The Moisture and the Problems: The Cost Table of the Water

Before the machines, the module fixes the arithmetic of the water, because the moisture is a measurable, accountable cost of the process:

• The moisture and the mill capacity: every extra percent of the feed moisture reduces the mill throughput: the module numbers: an air-swept ball mill fed above its drying capacity loses the production at the rate of the bound: the wet feed is the silent derating of the plant: the module: the mill capacity curves and the moisture: the two lines cross at the plant’s decision point;
• The evaporation cost: the latent heat of the water about 2,260 kJ per kilogram plus the sensible heating and the losses of the system, the practical 2,600–3,200 of the module: at the clinker rate of the plant, each percent of the feed moisture equals the delivered tonnes of the coal of the region: the module: the annual cost sheet of the moisture: the training: the numbers of the board;
• The downtime cost: the chutes, the screens, the feeders clogged by the sticky clay: the module: the wet material triples the cleaning calls and the stoppage minutes: the module’s table: the moisture is also a maintenance cost: the unexpected one;
• The chemistry trap: the moisture makes the proportioning lie: the wet clay fed at its weighed tons is fewer dry tons: the module: the moisture correction of the raw mix: the control that the mix module always counts, and this module makes explicit: the dry-basis calculation of the feeding;

The price chapter is the chapter that keeps the attention: the trainees of every region recognize their wet seasons in the tables of the module: the drying is not a utility, it is the economy of the raw department.

3. The Drying Principles: The Physics in the Plant Words

The module opens the theory of the drying without the heavy mathematics:

• The driving force: the evaporation needs the heat (to the water) and the carrier (the air or the gases that take the vapor away): the module: the drying rate rises with the temperature of the carrier and with its dryness, and falls as the material gets dryer: the falling-rate phase of the module;
• The heat sources of the plant: the module presents the family: the direct firing (the burners of the dryers), the kiln waste gases (the most economical), the cooler air and the waste heat: the choice of the module: the economics decide: the gases of the kiln dry the raw with heat that would otherwise be lost;
• The drying mediums: the air, the flue gases: the dew point and the saturation: the module: the bag of the humid gases: the dust collection of the dryers: the cyclone and the bag filter of the module’s systems;
• The temperature limits: the material temperature and the risk of the changes: the module: the drying is a process of the control, not a bonfire: the clay overheated changes its properties: the module’s bounds;

The physics of the module is the physics the operator uses daily: why the winter dries slower, why the humid air clogs the filter, why the waste-gas drying is the cheapest: the understanding of the drying becomes the understanding of the energy of the raw department.

4. The Rotary Dryers: The Classic Machines

The module devotes its first machine chapter to the rotary dryer, the classic of the wet plants:

• The construction: the inclined rotating cylinder, the lifters and the flights that cascade the material through the gas stream, the hot-gas inlet at the feed end (co-current) or the opposite (counter-current), the tires, the girth gear and the drive: the module: the anatomy of the drum;
• The co-current and the counter-current: the module compares: the co-current protects the material (the hottest gas meets the wettest material), the counter-current drives the deeper drying at the higher exit temperatures: the module: the sticky clay chooses the co-current: the module’s rule;
• The capacity and the sizing: the moisture in, the moisture out, the gas flow and the residence time: the module: the typical capacities and the specific volumes of the dryer: the sizing relations that the design offices reuse;
• The operations: the temperature control at the inlet and the outlet, the feed rate, the fuel of the direct firing, the exhaust fan and the collection: the module: the operator’s panel of the rotary dryer;
• The wear and the maintenance: the lifters and the shell, the seals, the refractory of the hot end: the module: the rotary dryer is a small kiln and shares its maintenance habits: the inspection of the module;

The rotary dryer chapter is the machine training of the module: the drawing, the operation and the maintenance: the trainee of the module recognizes the machine of his plant and the design of the others.

5. The Flash and the Mill Drying: The Systems of the Modern Plant

The modern cement plant rarely owns a separate dryer: the drying moved inside the raw mill, and the module presents the modern systems with the same care:

• The flash dryers: the pneumatic drying: the material entrained in the hot gas stream, dried in the seconds and separated in the cyclone: the module: the sticky materials and the dispersers: the dryer for the fines and the correctives;
• The drying in the raw mill (the air-swept mills): the kiln exit gases (200–350°C) sweep the mill, the raw meal grinds and dries in the same circuit: the module: the great economy: the waste heat of the kiln replaces the fuel of the dryer: the moisture capacity of the air-swept mill (about 8–14% of the feed): the module: the mill is the dryer of the modern plant;
• The vertical roller mills: the integral drying: the hot gases through the mill, the recirculation, the high drying capacity of the modern VRMs (15% and more of the feed moisture): the module: the modern line needs no separate dryer;
• The gas circuits: the bag filters of the mill, the recirculation and the balance: the module: the gas dew point and the condensation protection: the startup with the cold mill: the module’s start sequence;

The module covers the old and the new: the trainee of the modern line reads the mill-drying chapters as his own process, and the trainee of the older wet plant reads the rotary dryer chapter: the module serves the two generations and the transition between them.

6. The Drying in the Preheater: The Last Word of the Water

The module also explains where the remaining moisture meets its final end: the preheater of the kiln:

• The exhaust gases of the preheater tower: the gases leave the preheater at 250–400°C with the heat content that the raw mill consumes: the module: the integrated drying: the tower, the mill and the bag house form one energy system;
• The kiln feed moisture: the acceptable feed moisture of the preheater (typically below 1–2%), and the meaning of the wet feed to the tower: the module: the stability of the suspension and the preheater operation;
• The drying and the emission control: the water vapor in the gases and the condensation in the filters: the module: the dew-point management of the bag filters and the mills: the module’s tables;

The preheater chapter closes the water journey: the module shows the full cycle of the water in the plant: from the quarry rain to the stack vapor: the trainee sees the plant as the water-handling system it is.

7. The Control and the Quality of the Drying

The module teaches the control room of the drying:

• The moisture target: the moisture of the mill feed and the meal: the module: the target window of the feed (from the mill’s drying capacity) and the action limits: the moisture control of the day;
• The temperature control: the inlet and the outlet temperatures of the dryer and the mill gases: the module: the set points and the response: the operator’s panel: the loop of the drying;
• The feed control: the feed rate of the wet material against the drying capacity: the module: the overload of the wet feed is the first failure: the module: the feed and the temperature go together;
• The quality effects: the drying that preserves the chemistry and the grindability: the module: the overdried material wastes the energy, the underdried clogs the process: the window of the module;
• The reporting: the moisture reports, the energy per tone, the downtime: the module: the KPI of the raw department: the drying efficiency of the plant;

The control chapter is the operator’s chapter: the module gives the dials, the targets and the loops, and the simulator exercises of the series complete the training: the control of the drying is the control of the energy and the stability.

8. The Drying in the Complete Formation: The Module’s Position

In the series, the drying module closes the preparation chain: the raw materials (01), the mix calculation (02), the crushing (03), and now the drying (04): the chain that transforms the quarry rock into the dry, proportioned, sized raw feed: the next modules of the series (the grinding, the work index, the mill data) begin the milling chain: the module’s position is the hinge: the wet department ends, the dry department begins: the trainee who passes the module sees the change of the state of the material and understands why the plant is organized in the wet and the dry sections.

The package supports the module with its resources: the Excel tools of the drying calculations, the kiln and the mill courses that use the drying, the books of the process: the module is the classroom of the hinge, and the package is the library of the whole line.

9. The Energy Systems of the Drying: The Heat Economy

The drying consumes heat, and the module teaches the economics of the heat sources in the language of the plant’s energy balance:

• The waste-heat hierarchy: the cheapest dryer fuel is the heat the plant already owns: the kiln exhaust gases, the cooler vent air, the clinker cooler air: the module: the waste heat first, the direct firing last: the hierarchy of the module is the hierarchy of the modern plant’s decarbonization planning;
• The direct firing: the standby and the supplement: the fuel burners of the dryers for the wet peaks and the startups: the module: the fuel share of the drying stage: the alternatives: the module: the burner of the dryer is the same family as the kiln burners of the package;
• The heat recovery networks: the collectors and the loop of the gases, the preheating of the combustion air, the integrated systems of the plant: the module: the modern lines balance the gas matrix of the tower, the mill and the filter in one system;
• The energy KPI: the GJ per tone of the dried material, the evaporation efficiency: the module: the reporting and the benchmarking of the drying energy: the module’s forms;

The energy chapter is the partner of the environmental chapters of the package: the heat saved in the drying is the CO2 saved at the burner: the module gives the professional the energy vocabulary that the decarbonization discussions of the plant use every week.

10. The Dust Collection and the Housekeeping of the Drying Systems

No drying system exists without its dust collection, and the module treats the pair as one:

• The cyclones: the pre-collection: the coarse dust of the dryer and mill exhausts: the module: the cyclone efficiency and the loading;
• The bag filters: the final cleaning of the drying gases, the filter cloths, the pulse cleaning, and the danger of the condensation: the module: the bag house of the raw mill runs above the dew point: the temperature control of the module: the startup sequence: the fresh filter: the training;
• The water vapor and the corrosion: the acids of the flue gases with the water vapor: the module: the linings and the materials of the ducting: the corrosion protection of the cold-end systems;
• The dust recycling: the collected dust returns to the process feed: the module: the chemistry of the dust is the chemistry of the meal: the dust of the drying returns: the loop;

The collection chapter closes the environmental face of the drying: the module trains the operator to treat the filter as a production machine (the temperatures, the pulses, the leaks) and not as the afterthought: the filters of the drying systems are the lungs of the raw department, and the module teaches their care.

10. The Workshop and the Final Chapter of the Module

The module closes its body with the workshop that the series standardizes:

• The moisture determination in class: the oven-dried samples: the class computes the percentages and builds the day’s table: the practical of the module;
• The circuit diagram: the trainee draws the drying circuit of his plant (the crusher, the pile, the mill, the filter, the recirculation) and identifies the moisture control points: the module: the examination;
• The cost case: the annual cost of the moisture at the plant’s own rate: the table of the module: the case discussed in the class: the students present;
• The quiz: the ten questions of the moisture, the dryers and the controls: the answers of the series: the grading: the records of the training;

The workshop is the evaluation of the module, and the plant keeps the results in its training file: the module of the drying is completed when the class has drawn its own circuit and priced its own water: the training of the module is the training of the plant’s reality.

11. The Drying in the History of the Industry: The Wet and Dry Families

The module places the drying in the history of the industry, and it is a history that every cement man of the raw department benefits from recalling:

• The wet process: the raw materials ground with the water into the slurry of the 30–40% moisture: the drying happened in the kiln itself, with the enormous heat costs: the module describes the family: the plants of the wet process and their kilns with the internal chains of the drying zone;
• The semi-wet and semi-dry processes: the filter presses and the drying of the filter cake, the Lepol grate preheater: the module: the intermediate generations between the wet and the dry;
• The dry process with the integrated drying: the drying moved out of the kiln into the mill circuit: the heat of the kiln gases: the module: this is the world family of the modern line, and the module is its textbook;

The history chapter explains the plant’s own archives: the design decisions of the founders (the wet plant of the humid region, the dry line of the desert) are visible in the equipment of the module: the trainee who knows the families reads his plant’s story: and the module’s energy logic explains why the industry converged on the dry process with the waste-heat drying: the economy of the water built the modern cement: the module tells the tale with the numbers that the plant still uses: the drying became the invisible stage of the modern line, and the invisible stages are exactly the ones the trained eye must read.

12. Frequently Asked Questions

Is the drying module relevant to a plant with a dry quarry?

Yes: even the dry-region plants face the moisture of the clay and the rainy weeks, and every plant of the world owns the kiln-gas circuits of the mill drying: the module’s control chapters apply to every line: the moisture is never zero, and the discipline of the drying never sleeps.

Why does the module cover the rotary dryers if the modern lines do not have them?

Because the plants of the world are a mix of the generations: thousands of the wet-process and the semi-wet lines still run the rotary dryers, and the engineers of the modern lines maintain and retrofit the older equipment: the module prepares the professional for the complete family: the knowledge of the rotary dryer is the knowledge of the evolution of the plant.

What are the typical moisture numbers of the module?

The ballparks of the module: the limestone feed 1–6%, the clay 8–25%, the air-swept mill drying capacity 8–14%, the VRM capacity 15% and more, the kiln feed below 1–2%: the evaporation heat about 2,600 kJ per kilogram of the water: the plant’s own numbers depend on its region and its machines, and the module teaches the measurement that finds them.

What does the module take as the target moisture?

The meal itself is a dry powder: the module controls the moisture at the gate: the mill feed window first (the drying capacity of the mill system), then the kiln feed below the 1–2%: the plant measures the feed moisture daily, watches the pile weights and corrects the mix on the dry basis: the module’s control chapter is the discipline of the measurement: the measured percent, the reported number, the corrected feed.

Is the drying module needed for the desert plants?

Yes, even in the desert: the clays of the region carry their moisture, the seasons change, and the kiln gases of every plant exchange the heat through the mill drying circuits: the desert plants run the same systems at the lower loads, and the engineers who move between the regions of the group take the module with them: the moisture discipline travels with the profession.

Does the module cover the semi-wet lines of the group?

The module keeps the family: the semi-wet lines with the filter cake and the drying additions of their process appear in the module’s circuits, and the maintenance notes of the module apply: the trainee of the semi-wet line reads the module with the filter legacy in mind, and the package’s kiln courses complete the picture: the module is written for the whole family of the wet-to-dry spectrum, and the plants of each family find their chapter.

How do I get the module?

The module arrives with the Complete Cement Technical Package: the 931 files: the courses of the series, the books, the Excel tools and the presentations: the one-time 249.99 dollars via the PayPal: the instant download: the drying module and the complete preparation chain, from the quarry to the silo: the lifetime.

13. Conclusion

The drying of the raw materials: the module of the water: 33 pages that give the plant the moisture awareness: the measurement, the physics, the dryers, the mill-drying systems, the control and the energy: the module of the hinge between the wet and the dry departments: in the Complete Cement Technical Package it stands in its series, supported by the tools and the courses of the whole line: for the one-time 249.99 and the lifetime: the plant, the operator, the professional: the water is understood, the heat is saved, and the raw feed arrives dry: the module of the drying, the quiet power of the raw department.

For the trainee who closes the module with the quiz passed: the raw preparation chain of the package is now complete in his head: the raw materials, the mix, the crushing, the drying: the four modules that prepare the feed of the mill and the kiln: the ladder of the package then continues with the grinding, the kiln and the cement: the drying module was the hinge, and the trainee has crossed the hinge: the water, the heat and the machines of the drying are no longer the mystery of the department: they are the discipline he owns: the module of the water, mastered, is the module of the energy mastered.

The drying of the raw materials handles the moisture of the limestone, the clay and the additives before the grinding: this module covers the dryers, the hot gas supply, the drying capacity calculations, the energy consumption and the control of the residual moisture for the stable raw mill operation and the kiln feed quality.

This file is part of the Complete Cement Technical Package (931 files) available from cementequipment.org. Respective rights holders; library copy for the licensed single user.